I can't really see how you can always give yourself a half-decent chance of a good landing without changing/adjusting the power in the final descent.
Okay, I'll bite. It's true that the approach technique that's currently taught in powered flying is to approach *below* the zero-power glidepath, and use engine power to maintain your desired glide path. But that's by no means the only technique. You can also approach *above* the zero-power glidepath, reduce the throttle to idle and vary the drag (flaps, airbrakes, sideslips, forward slips, s-turns, you name it) to maintain the desired glide path. Gliders do this all the time and although this technique might not be desirable in a busy (power) circuit, it's a good technique to master.